This invention relates to the identification of modules (e.g. boards) and their existence in a modular processor system, such as for use in a communications system.
1. Summary of the Prior Art
Many types of electrical equipment exist which comprise a main board and a number of "option"boards, i.e. functional add-on boards added by the user in a "pick and choose" manner to suit his application. Examples are the VMEbus microprocessor system. There is a need to identify automatically boards, for example printed circuit boards, modules and the like that are installed in the system and there is a need for the main unit to "learn" the system configuration.
In the field of battery chargers, it is known to incorporate a resistor in the battery and for the battery charger to read the value of the resistor to determine the type of battery and therefore the charging parameters required. Such an arrangement is shown in EP-A-0394074. Only one battery is connected to the charger at any one time.
2. Summary of the Invention
According to the invention there is provided a processor system comprising a control module and a variety of subsidiary modules connected to the control module by means of a bus and an analog connector line. The control module comprises an analog-to-digital input for receiving a signal on the analog connector line and each of the subsidiary modules comprises an analog element and switch means connected for selectively switching the analog element to provide an analog signal on the analog connector line in response to a control signal received from the control module.
The invention provides the advantage that a control signal provided to a subsidiary module from the control module activates the switchable means, so causing a change in the level on the analog connector line, thus indicating to the control module the presence of the subsidiary module.
It is preferred that a number of subsidiary modules have different functions and each has an analog element representative of its function, whereby subsidiary modules with the same or similar functions have the same analog element.
The analog element may be a resistance which, when switched causes a change in the voltage level on the analog connector line, the change being dependent on the value of the resistor, which is in turn indicative of the function of the subsidiary module.
A preferred embodiment of the invention will now be described by way of example only, with reference to the drawing.